(a) Field of the Invention
The present invention relates to timer mechanisms for time delay relays, such as used in industrial control circuits for controlling motors, machinery, and manufacturing methods and systems. In the operation of control relays it is often desirable to delay the opening or closing of one or more sets of contacts after energizing or deenergizing the relay electromagnet. To accomplish the delay, a timer mechanism is used that has a timing function initiated upon an operation of the electromagnet, and the present invention relates to a pneumatic timer of this type.
(b) Description of the Prior Art
A typical form of pneumatic timing mechanism is shown in U.S. Pat. No. 3,249,716 issued May 3, 1966 and entitled "Time Delay Device". It contains a bellows with an operating button that cooperates with a set of levers for operating associated contacts. The bellows is held in a collapsed position until an associated electromagnet is either energized, or deenergized, at which time the bellows is free to expand at a timed rate. Upon completing its expansion, the bellows trips a contact actuating mechanism to obtain the desired time-delayed operation of associated relay contacts.
Air is admitted to the bellows through a needle valve that is adjusted in its position to control the period of delay for contact operation. To make an adjustment, the needle is moved lengthwise of itself, and by observing the axial position of the needle one has an indication of the time period for the delay in contact actuation. Such prior art construction requires the needle to be exposed for observation of its position, and a long linear scale is required for reading the position of adjustment of the needle. It is also a part of such construction to arrange the needle valve in a direction perpendicular to the bellows. This is necessary to accommodate the manually engageable adjustment member on the top of the device, where it may be readily manipulated whenever it is desired to reset the period of time delay.